Since a medical tape (adhesive tape) which consists of a substrate and a medical pressure-sensitive adhesive composition is used by adhering or winding itself around the skin (corneous layer), as well as having moderate adhesion to the skin; it is preferable to have a proper peel property that does not cause skin stimulus or a rash by peeling damage to the corneous layer of the skin.
Therefore, in recent years, the medical pressure-sensitive adhesive composition and the medical tape have been proposed in consideration of a good balance between the skin adhesion property and the peel property.
For example, JP6-4533B(JP62-77316A) has disclosed the external application medicine component in which a polymer alloy is laminated on a substrate, wherein the polymer alloy has a number average molecular weight of 90,000 to 250,000 and the ratio (Mw/Mn) of a weight average molecular weight (Mw) to the number average molecular weight (Mn) of 6 to 12, and consists of 80 to 99.5 percent by weight of acrylic polymer and 0.5 to 20 percent by weight of acrylic oligomer having a number average molecular weight of 700 to 5,000.
Moreover, JP3-70685B has disclosed the pasting agent in which a pressure-sensitive adhesive layer containing a medicament and an (meta)acrylic acid ester-vinyl pyrrolidone random copolymer that contains 1 to 60 percent by mole of vinyl pyrrolidone is laminated on one surface of a substrate sheet.
However, each of the external application medicine component has been disclosed in JP6-4533B and JP3-70685B is substantially a single formulation, and moreover, because it is not cross-linked, it causes a shortfall of cohesive force or an excessive restriction of the additional amount of an acrylic oligomer, and the control of the corneous picking area ratio becomes difficult. Also, the problem of poor re-adhesion property is witnessed, as represented in the result of the comparison between comparative example 9 and the present invention as shown in FIG. 2. Moreover, since the number average molecular weight of the acrylics polymer to be used is low, the problem is witnessed in that the cohesive force becomes even more insufficient and the adhesion to the skin becomes poor.
Therefore, various acrylic adhesive compositions that contain an acrylic acid ester polymer and a liquid component or pasting agents including them have been known.
For example, JP5-139960A has disclosed the pasting agent, which has the adhesive layer made from the cross-linked polymer on one side of a substrate. This pasting agent is characterized by the 180° peel adhesion strength that is 20 to 180 g/12 mm in width, when the adhesive layer is bonded together. More concretely, this pasting agent contains an acrylic acid ester polymer and a liquid plasticizer which is compatible with this polymer, as an adhesive layer.
Moreover, JP2971998B (JP5-65460A) has disclosed the acrylic pressure sensitive adhesive sheet which has the maximal moving distance such as 0.5 to 6 times of the adhesion layer's thickness due to a shear deformation under shear stress, which contains acrylic acid ester polymer and a liquid component, for example, a plasticizer or a surfactant, which is compatible with the acrylic acid ester polymer on at least one surface of a support, and which is an elastic body that does not cause cohesive failure or interface failure when a shear stress is applied.
However, in the acrylic pressure-sensitive adhesive composition and the pasting agent including the same, which have been disclosed in the JP5-139960A and JP2971998B(JP 5-65460A), the problem is witnessed in that the re-adhesion property is poor, as represented in the result of the comparison between comparative example 11 and the present invention which are shown in FIG. 2. More concretely, since the compatibility between the acrylic polymer and the liquid component or a plasticizer that is added to the acrylic polymer is inadequate, the liquid component may migrate to the surface of the adhesion layer, and skin stimulus becomes high. On the other hand, the problem is witnessed in that proper peel adhesion strength is not obtained when the adhesion is tried again, after adhesion to the skin and peeling off have once been performed. Therefore, to solve the above problems, the inventors of the present invention have carried out several experimental studies on medical tapes including specific acrylic polymers and specific acrylic oligomers. As a result, the intermediate composition was prepared in advance; this composition was composed of an acrylic polymer having a predetermined number average molecular weight (Mn) including a predetermined amount of a specific type of acrylic oligomer having a predetermined number average molecular weight (Mn). Then, by crosslinking the intermediate composition, it was able to provide a medical tape that had an excellent re-adhesion property and that caused only slight skin stimulus, while at the same time, the wettability against the skin was kept high, and a predetermined peel adhesion strength was maintained. Consequently, the present invention has been completed.
Thus, an objective of the present invention is to provide a medical pressure-sensitive adhesive composition that is excellent in re-adhesion property, while the peel adhesion property is good and skin stimulus is low, to provide a process for producing the same, and to provide a medical tape in which such a medical pressure-sensitive adhesive composition is formed on a substrate.